Molded workpieces of any three-dimensional form, including polyolefin-based moldings, fibers and films, are used on a very wide scale in practice. An important problem area here is improving the surface properties of these structurally nonpolar hydrocarbon components. Thus, the poor adhesion of coatings and adhesives is a central problem which has remained unsolved for decades despite numerous attempts to find a solution.
It is known that the compatibility of plastic surfaces with coatings and adhesives can be improved, for example, by oxidative aftertreatment processes, such as corona or plasma treatment. In processes such as these, the surface of the plastic is oxidized or chemically modified in the presence of gases and discharges, so that certain surface properties of the plastic can be modified. However, apart from their high energy consumption, processes such as these always involve an additional step and lead to ozone emissions in the manufacture of plastic parts. In addition, chemical pretreatment processes, including for example treatment with fluorine or chlorine gas, with chromosulfuric acid or fluorosulfonic acid, etc., have also been known for some time.
EP-B-372 890 describes polyolefin- or polyester-based fibers with a lubricant adhesively applied to their surface. This lubricant comprises a mixture of (1) fatty acid diethanolamide, (2) a polyether-modified silicone, (3) a sorbitan fatty acid ester and (4) a metal salt of an alkyl sulfonate. Components (1) to (4) are present in special quantity ratios. According to page 3, lines 20 to 26, the mixture of components (1) to (4) is applied to the surface. The technique by which the mixture containing the four components is applied to the surface of fibers is described in detail on page 4, lines 6 to 9. The application techniques mentioned include a) the use of rollers, b) spraying and c) immersion. Accordingly, the process according to EP-B-372 890 is a process in which a mixture of components (1) to (4) is applied to the surface of polyolefin moldings in an additional process step. Accordingly, the expression xe2x80x9cadhesively applied to the fiber surfacexe2x80x9d used in claim 1 of EP-B-372 890 may be clearly interpreted by the expert to mean that any adhesion involved is loose and temporary, for example in the form of relatively weak adhesion forces, and cannot in any way to be considered to represent permanent anchorage.
In view of the very widely used traditional chemical aftertreatment processes, such as corona and plasma treatment, it is known to the expert that no exact statements can be made as to the various processes involved. However, it has been established that oxidative surface changes occur and result in the formation of certain xe2x80x9cactive centersxe2x80x9d. Unfortunately, their concentration generally decreases with time so that the pretreatment effect also is only in evidence for a certain time, generally not more than 72 hours (cf. for example, Klaus Stoeckert (Editor), xe2x80x9cVeredeln von Kunststoff-Oberflxc3xa4chenxe2x80x9d, Munich 1974, page 137).
One feature common to all the known processes is that, in general, the desired surface effects are only temporarily present.
EP-B-616 622 relates to extrudable compostable polymer compositions comprising an extrudable thermoplastic polymer, copolymer or mixtures thereof containing a degradation-promoting system of an auto-oxidative component and a transition metal. The auto-oxidative system comprises a fatty acid, a substituted fatty acid or derivatives or mixtures thereof, the fatty acid having 10 to 22 carbon atoms and containing at least 0.1% by weight of unsaturated compounds and at least 0.1% by weight of free acid. The transition metal is present in the composition in the form of a salt in a quantity of 5 to 500 ppm and is selected from the group consisting of cobalt, manganese, copper, cerium, vanadium and iron. In the form of a film around 100 microns thick, the composition is said to be oxidatively degradable to a brittle material over a period of 14 days at 60xc2x0 C. and at a relative air humidity of at least 80%.
WO 97/12694 and WO 98/42776 describe the use of amphiphiles for permanently improving the adhesive and/or coating compatibility of polyolefin-based moldings, fibers and films in which a mixture containing (a) predominantly one or more polyolefins, (b) one or more migratable amphiphiles and (c) of one or more transition metal compounds is subjected in the usual way to molding, for example by extrusion, at temperatures in the range from 180 to 320xc2x0 C. It is disclosed that dialkanolamides of unsaturated fatty acids, for example oleic acid diethanolamide or linoleic acid diethanolamide, are particularly suitable for use as component (b). So far as the nature of component (c) is concerned, WO 97/12694 makes particular mention of Co, Zr, Fe, Pb, Mn, Ni, Cr, V and Ce while WO 98/42776 refers in particular to Ti and Sn as the transition metal present in that component.
The present invention relates, in general, to the use of amides of aromatic carboxylic acids for permanently improving the adhesive and/or coating compatibility of polyolefin-based moldings, fibers and films.
The problem addressed by the present invention was to provide auxiliaries with which the adhesive and/or coating compatibility of polyolefin-based moldings, fibers and films could be lastingly and permanently improved. In other words, the object of the invention was to provide auxiliaries for permanently improving the affinity of polyolefin surfaces for adhesives and/or coatings. More particularly, the object of invention was to make it possible to establish high-strength bonds which would rule out unwanted adhesive failures and would ensure that the adhesive joint could only be destroyed by cohesive failure or by combined cohesive/adhesive failure. In particular, the effectiveness of the amphiphiles known from the prior art in permanently improving the adhesive and/or coating compatibility of polyolefin-based moldings, fibers and films would be quantitatively improved.
The present invention relates to the use of carboxylic acid amides for permanently improving the adhesive and/or coating compatibility of polyolefin-based moldings, fibers and films, a mixture containing
a) predominantly one or more polyolefins,
b) 0.01 to 20% by weightxe2x80x94based on the polyolefinsxe2x80x94of one or more carboxylic acid amides and
c) 0.01 to 1000 ppm of one or more transition metal compoundsxe2x80x94metal content of the transition metal compounds, based on the polyolefinsxe2x80x94being subjected in known manner to molding by extrusion, calendering, injection molding, blow molding and the like at temperatures of 180 to 330xc2x0 C., with the proviso that the carboxylic acid amides b) are selected from the class of amides of aromatic carboxylic acids
xe2x80x9cTransition metalsxe2x80x9d in the context of the present invention are any transition metals in the narrower sense (cf. for example Rxc3x6mpps Chemie-Lexikon, Stuttgart 1977, pp. 3717) and, in addition, the metals tin (Sn) and lead (Pb).
The amides of aromatic carboxylic acids b) to be used in accordance with the invention are derived from aromatic carboxylic acids. These are compounds which have an aromatic skeleton that may optionally be substituted by one or more alkyl groups, one or more carboxyl functions being present on this skeleton and/or at the alkyl substituents.
In principle, the aromatic skeleton of the carboxylic acids on which the compounds b) are based is not subject to any limitations. Thus, the aromatic structural unit of the compounds b) may be derived from benzene although it may equally well be derived from a polycyclic compound such as, for examle, naphthalene, anthracene, etc.
Examles of particularly suitable aromatic carboxylic acids on which the compounds b) are based are benzoic acid, phthalic acid, terephthalic acid.